1. Field of the Invention
The present invention relates to a chair seat-back mechanism and, more particularly, to an adjustable seat-back mechanism for secretarial chairs and the like for allowing facilitated vertical adjustment of the seat-back while at the same time providing a very reliable, simply-constructed mechanism which can be manufactured inexpensively.
2. Description of the Prior Art
The chairs with which the present invention is concerned are of the relatively simple type such as those used by secretaries and draftsmen, for example, and generally include a base or stand, a seat mounted to the base, a bar or tubular member attached to the seat or base and a seat-back fastened to the bar. Because of the varying sizes of the people who will use the chair, the seat-back is generally adjustable to allow for universal usage.
Many prior art chairs comprised a threaded handle which engaged the bar member to hold the seat-back in a particular position by a friction engagement between the handle and the bar member. While a great many chairs were and still are so constructed; there are major disadvantages, the most important of which is the difficulty in making adjustment. This is due to the excessive force necessary to secure the seat-back in a desired position. For example, most women cannot easily adjust their chairs because they physically are unable to provide sufficient torque to turn the handle. If sufficient torque is not used, then the seat will slip downwardly and refuse to stay in position.
An example of a more recent system which eliminates some of the earlier problems is shown in U.S. Pat. No. 3,295,888 in which the adjustment system includes a small steel ball that is moved between arcuate slots by a spring-operated positioning member. While the problem of insufficient torque appears solved, other problems still exist, including the complexity of such systems and the difficulty and expense of manufacture.